The visual world contains more information than the brain can process. Fortunately, we have some ability to influence which sources of information receive processing priority through the mechanism of selective attention, and this ability is critical for daily life. While much research has focused on the effects of attention on information processing, relatively little remains known about how attention states are established. This is because clear effects of attention preparation at the level of single neurons have not been forthcoming. Recently, movement preparation has been linked to activity patterns that can be identified by analyzing dozens of neurons together. Such `high-dimensional' analyses have not been applied to sensory brain areas however, and we reasoned that a similar approach may overcome the barriers to progress in explaining attention preparation in sensory cortex. The goal of this research project is to apply high-dimensional analyses to the neuronal activity in sensory cortex in order to characterize how attention states are established. We have developed a carefully titrated research strategy that will achieve this overarching goal through three systematic and specific aims. We will begin by identifying the activity patterns in visual cortex that correlate with attention and inattention, both in the context of attention to spatial locations and in the context of attention to visual features. We will then add a layer of complexit by analyzing neuronal activity recorded from both visual cortex and frontal cortex -a presumed source of attention control signals -to identify the processes that drive these preparatory attention states. Finally, to test the causal nature of the neuronal correlates identified by the preceding two aims, we will use microstimulation in frontal cortex in an effort to mimic the neural and behavioral effects of attentional preparation. Since this is a career development award, another major goal of this project is the training of Dr. Adam C. Snyder in the high-dimensional analysis methods (under the mentorship of Dr. Byron Yu of Carnegie Mellon University) and experimental techniques (under the mentorship of Dr. Matthew Smith of the University of Pittsburgh) required for the achievement of the research aims, as well as the professional practices that will be needed throughout his career as an independent scientist. At the end of this project, Dr. Snyder will have received first-rate training in the analysis of high-dimensional datasets and practices of primate electrophysiology, strengthening his foundation as an innovative and successful neuroscientist. From a scientific perspective, we will have developed a new model of attention preparation that will overcome a long-standing barrier to progress in attention research. This advancement will not only benefit attention research itself, but will provide a framework for future investigations of other brain processes that involve feedback modulation of sensory processing, such as learning and memory. An understanding of the functioning of attention in health individuals is essential to guide potential therapeutic interventions in disorders involving deficits in attention, including autism, schizophrenia and attention deficit disorder.